1. Field of the Invention
The present invention relates to an anodization-adapted aluminum alloy and a plasma-treating apparatus made of the anodization-adapted aluminum alloy. More particularly, it relates to such an aluminum alloy and plasma-treating apparatus for service in both corrosion and plasma treatment environments.
2. Description of the Related Art
In a prior art plasma-treating apparatus for use in producing semiconductors and liquid crystal, corrosive gases and irradiating plasma heavily damage non-processed aluminum. In addition, metallic elements scattered from the material adversely affect an article to be processed such as a silicon wafer. In order to overcome such inconveniences, materials as defined by the JIS Standard, such as a 5000-series aluminum alloy (hereinafter called a “5000-series alloy”) and a 6000-series aluminum alloy (hereinafter called a “6000-series alloy”), are in common uses, in which instance, the 5000- and 6000-series alloys are subjected to hard anodized aluminum treatment (hereinafter referred to as “anodization”).
In recent years, causes such as micro-wiring patterns in a semi-conductor device, high-density plasma to be used, and high-corrosive gases to be used have rendered it conspicuous as an important issue to avoid deterioration and contamination of members used under plasma environments.
FIG. 5 illustrates amounts of impure elements contained in aluminum alloys, in comparison with aluminum having a high purity of 99.9 wt % (3N) or greater.
As illustrated in FIG. 5, commercially available 5052- and 6061-alloys contain considerable amounts of impure elements, when compared with the high-purity aluminum alloy. In the 5000- and 6000-series alloys, the 5052- and 6061-alloys are most widely used as materials of a plasma electrode plate and a plasma chamber. These impure elements are likely to cause defects in an anodized film. In addition, the impure elements may reside in the anodized film. This causes contamination because the impure elements residing in the anodized film are likely to fall onto an article to be processed such as a silicon wafer during plasma treatment.
In order to avoid lodging the impure elements in the anodized film, it is believed that aluminum having a high purity of 3N or greater is preferably used as a material. However, the plasma electrode plate and the plasma chamber need the strength of some 200 to 300 N/mm2, which is similar to the strength of the 5000- or 6000-series alloy. Accordingly, the high-purity aluminum smaller in strength than the 5000- and 6000-series alloys is difficult to solely employ.
In order to meet such requirements under the plasma circumstance, it has been proposed to use an aluminum alloy having Mg and Si added to high-purity aluminum (refer to published Japanese Patent Application Laid-Open No. 10-88271) and an aluminum alloy having Mg, Si, and Cu added to the high-purity aluminum (refer to published Japanese Patent Application Laid-Open No. 2001-220637).
The hitherto proposed aluminum alloys satisfy, to a certain degree, the above requirements under the plasma environment. In such aluminum alloys, the added Mg and Si precipitate Mg2Si to increase the strength of the high-purity aluminum. In this instance, minute Mg2Si is precipitated in the anodized film.
However, the minute Mg2Si precipitated in the film forms air gaps in the film. The formed air gaps inconveniently render the film susceptible to spallation during plasma irradiation, and thus inconveniently reduce the corrosion resistance of the aluminum alloy.
In the aluminum alloy taught in the published Japanese Patent Application Laid-Open No. 2001-220637 as previously discussed, the added Cu results in high-density Cu around the precipitated Mg2Si to form air gaps during anodizaiton. The formed air gaps alleviate the occurrence of cracks in the film. However, as previously discussed, the film is preferably devoid of such void spaces.
In general, members used under the plasma circumstance are costly. Accordingly, each of the costly members is removed when being worn to some degree. The film is stripped from the worn member. The worn member free of the film is again anodized, thereby forming a new film on the re-anodized member. In this way, the members are often reused. In the aluminum having Mg2Si precipitated, however, components under the plasma circumstance are heated to coarsen Mg2Si in the material. The coarsened Mg2Si inconveniently results in defects in the film and reduced corrosion resistance of the aluminum during anodization-caused film formation.